Direct Q -Value Determination of the β − Decay of Re 187

The cyclotron frequency ratio of ${^{187}\\mathrm{Os}}^{29+}$ to ${^{187}\\mathrm{Re}}^{29+}$ ions was measured with the Penning-trap mass spectrometer PENTATRAP. The achieved result of $R=1.000\\text{ }000\\text{ }013\\text{ }882(5)$ is to date the most precise such measurement performed on ions. Furthermore, the total binding-energy difference of the 29 missing electrons in Re and Os was calculated by relativistic multiconfiguration methods, yielding the value of $\\mathrm{\\ensuremath{\\Delta}}E=53.5(10)\\text{ }\\text{ }\\mathrm{eV}$. Finally, using the achieved results, the mass difference between neutral $^{187}\\mathrm{Re}$ and $^{187}\\mathrm{Os}$, i.e., the $Q$ value of the ${\\ensuremath{\\beta}}^{\\ensuremath{-}}$ decay of $^{187}\\mathrm{Re}$, is determined to be 2470.9(13) eV.